The invention may be applied in direct-injection motor vehicles having an exhaust gas after-treatment device in the form of a particle filter, in particular a diesel particle filter (DPF), for storing soot emissions.
In order to estimate the charging or quantity of particles stored in a particle filter, an emission model for the supplied gas is conventionally taken as a basis in situations in which it is not possible to directly measure the stored charging.
Although, in the case of a diesel particle filter, in principle a differential pressure sensor (DP sensor) is conventionally used to estimate the soot charge, it can occur, depending on the charging state, that there is no longer any correlation between the differential pressure and the soot charge, as this correlation typically decreases as charging increases. Accordingly, at the same time as estimating the soot charge, a model is applied for the supplied gas containing the soot particles in order to determine the soot charge via an additional route or as a secondary estimation, the soot charge being furthermore estimated primarily via the differential pressure sensor. The estimated soot rate is then corrected with regard to the passive/active soot regeneration and integrated for estimating the soot charge.
However, the possibilities for measuring the soot rate in the exhaust gas or at the output of the engine by means of vehicle-side (on-board) sensors are limited and have not yet reached a mature stage of development. In addition, such measuring of the soot rate leads to an increase in the costs as a consequence of the additionally required sensor.
Against the foregoing background, it is an object of the present invention to provide a particle filter and a method for operating a particle filter, which allow, at comparatively low cost, the prompt initiation of regeneration of the particle filter or robust detection of the quantity of particles stored in the particle filter.
This object is achieved by the method and device according to the present invention.
A method according to the invention for operating a particle filter having at least one filter portion forming an open filter system and also a heatable particle collecting element which is arranged adjacently to this filter portion and comprises a material having temperature-dependent electrical resistance, includes the steps of heating the particle collecting element; and measuring the electrical resistance of the particle collecting element.
As a consequence of the heating of the particle collecting element, soot particles, which accumulate on the particle collecting element after charging of the filter portion forming the open filter system, are regenerated or burned. If now in this case the amount of soot accumulated on the particle collecting element exceeds a predefined threshold value, this may be determined by way of a decrease in the electrical resistance of the particle collecting element, allowing, at low cost, the prompt initiation of regeneration of the particle filter or robust detection of the quantity of particles stored in the particle filter.
According to a preferred embodiment, the particle filter has, in addition to the filter portion forming an open filter system, a further filter portion forming a closed filter system.
Preferably, the further filter portion forming the open filter system is arranged in an edge region of the particle filter. This has the advantage that the particle collecting element is charged last with soot particles, as the preferred flow path runs first through the central region of the particle filter, before the flow is guided to the edge region of the particle filter.
According to a preferred embodiment, the particle collecting element has a grid-like geometry for efficient accumulation of the particles.
According to a further aspect, the invention relates to a particle filter for filtering particles from the exhaust gas stream of an internal combustion engine, the particle filter having at least one filter portion forming an open filter system and also a heatable particle collecting element which is arranged adjacently to this filter portion and comprises a material having temperature-dependent electrical resistance.
Further embodiments may be inferred from the description and also the sub-claims.